The principal limitations of percutaneous techniques to replace the aortic valve principal are detailed visualization and durable prostheses. This study investigated the use of real-time magnetic resonance imaging to provide precise anatomic detail and visual feedback to implant a proven bioprosthesis. [unreadable] [unreadable] Via a minimally invasive approach using real-time MRI guidance 14 pigs underwent off-pump aortic valve replacement. MR imaging was used to precisely identify critical anatomic landmarks. Additional intraoperative perfusion, flow velocity and functional imaging were used to confirm adequacy of placement and function of the valve.[unreadable] [unreadable] Under real-time MR imaging, multiple oblique planes were prescribed. Enhanced by the use of an active (i.e. MR signal receiving loopless antennae) marker wire, this imaging allowed correct placement and orientation of the prosthetic valve. Via a transapical approach a series of bioprosthetic aortic valves (21-25mm) were inserted. The time to implantation after the placement of the trocar to deployment of the valve was less than ninety seconds (77 + 12). In addition to anatomic confirmation of adequate placement of the prosthetic valve in relation to the aortic annulus and the coronary arteries, functional confirmation of the valve and left ventricle was also obtained with MR imaging. Intraoperative first pass perfusion scanning documented adequacy of myocardial blood flow after valve placement. Phase velocity confirmed adequate opening of the prosthetic valve leaflets and lack of valvular or paravalvular regurgitation. [unreadable] [unreadable] Real-time MR imaging provides excellent anatomic detail and intraoperative assessment that permits placement of durable valve prostheses on the beating heart without the limitations of percutaneous approaches.